From: "H. Peter Anvin" <hpa@zytor.com>
To: "J.A. Magallon" <magallon@unizar.es>
Cc: "Linux-Kernel, " <linux-kernel@vger.kernel.org>
Subject: Re: Opteron box and 4Gb memory
Date: Thu, 25 Oct 2007 14:58:10 -0700 [thread overview]
Message-ID: <47211172.9070606@zytor.com> (raw)
In-Reply-To: <20071025230904.03d5f46a@werewolf>
J.A. Magallon wrote:
> Hi...
>
> I have some Quad-Opteron boxes with 4Gb memory and two of them are
> running two different Linux distros.
>
> Box one sees 4Gb of memory, but box two just sees 3.
> Their mtrr setups are different:
>
> Why ? Is it a bios setup problem ? A kernel problem ?
> grep HIGHMEN in configs for both kernels does not give anything, so
> I still understand less this thing...
>
It would depend on how the BIOS programmed the memory controllers. For
32-bit (and lots of device) compatibility, a memory hole is required
below 4 GB. Not all memory controllers can remap memory in the 3-4 GB
range above the 4 GB memory; I'm not sure if that varies with the
different Opteron processors.
Also, if you run a 32-bit distribution, you need to have HIGHMEM_64G
enabled in the kernel.
-hpa
next prev parent reply other threads:[~2007-10-25 21:58 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-10-25 21:09 Opteron box and 4Gb memory J.A. Magallon
2007-10-25 21:58 ` H. Peter Anvin [this message]
2007-10-25 22:44 ` J.A. Magallón
2007-10-26 8:08 ` Arne Georg Gleditsch
2007-10-25 22:45 ` Rafael J. Wysocki
2007-11-04 23:18 ` J.A. Magallón
2007-11-05 18:10 ` Lennart Sorensen
2007-11-05 18:45 ` J.A. Magallón
2007-11-05 18:50 ` Lennart Sorensen
2007-11-05 23:03 ` J.A. Magallón
2007-11-08 18:08 ` Lennart Sorensen
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